Account:: namespace simplifications and cleanup (#2110)

* Flatten Holding model

* Flatten balance model

* Entries domain renames

* Fix valuations reference

* Fix trades stream

* Fix brakeman warnings

* Fix tests

* Replace existing entryable type references in DB

test/controllers/categories_controller_test.rb

@@ -3,7 +3,7 @@ require "test_helper"
 class CategoriesControllerTest < ActionDispatch::IntegrationTest
   setup do
     sign_in users(:family_admin)
-    @transaction = account_transactions :one
+    @transaction = transactions :one
   end
 
   test "index" do